530 Invasive Stink Bugs and Related Species (Pentatomoidea)
other heteropteran species (Musolin and Saulich 1997). Recently, Niva and Takeda (2003) noted that in
Halyomorpha halys, short day accelerated nymphal development, whereas long day accelerated repro-
ductive maturation. The two types of photoperiodic responses at different stages may help maintain the
univoltinism of H. halys in the field, assuring the right timing for diapause and reproduction.
As with diapause induction, there must be some (preceding) stages that are sensitive to the cue induc-
ing this response (i.e., day length). For some species, these stages already are known. Thus, in the stink
bug Eysarcoris lewisi, acceleration or retardation of further nymphal growth is controlled by the photo-
periodic conditions experienced by the nymphs during the third instar, whereas the physiological state
(reproduction versus diapause) is controlled by conditions experienced only by nymphs during the fifth
instar or adult stage (Hori and Kimura 1993).
However, despite its clear adaptive significance, photoperiodic control of growth rate is not a universal
phenomenon in pentatomoids. Nymphs of some bugs grow faster under long-day conditions; moreover,
responses to day length may be directly opposite in different populations of the same species. Such differ-
ences were found, in particular, between populations of the sloe bug, Dolycoris baccarum, from Norway
and Japan (Conradi-Larsen and Sømme 1973, Nakamura 2003) and between populations of Nezara
viridula from Egypt and Japan (Ali and Ewiess 1977, Musolin and Numata 2003a). These examples show
that this trait can manifest itself at the population level, ensuring a high level of adaptation of the local
population to specific living conditions, and that seasonal adaptations can differ between populations.
At the same time, in some species, the nymphal growth rate does not depend on photoperiodic condi-
tions. For example, no distinct relations between the durations of nymphal stadia and photoperiodic con-
ditions were observed in Podisus maculiventris (Goryshin et al. 1988b). In Picromerus bidens (Musolin
and Saulich 1997, 2000), the effect of day length was small.
The physiological mechanism underlying this adaptation still has not been studied sufficiently.
Further research will be necessary to understand the exact nature of the effect of day length (accelera-
tion of development under certain conditions or retardation under other conditions) and the relationships
between these phenomena and winter or summer diapauses.
11.7.4 Seasonal Polyphenism
The external appearance of individuals of the same species and developmental stage can change season-
ally in some insect species. These changes can happen during the ontogenetic development of the same
individuals or occur in representatives of different generations of the same species. Such cases often
are difficult to notice and classify, and genetic and physiological mechanisms behind these changes are
poorly understood. However, diversity of such forms often are described in terms of polymorphism or
polyphenism.
Polymorphism usually is understood as the presence in a population of two or more distinct pheno-
types (morphs, forms) at the same ontogenetic stage (discontinuous variation; Kennedy 1961; Walker
1986; Nijhout 2003; Saulich and Musolin 2007a,b; Simpson et al. 2011; Rogers 2015). Polymorphism
can be divided into:
- genetic polymorphism (different phenotypes are produced by different genotypes), and
- environmental, or ecological polymorphism, or polyphenism, or conditional poly-
phenism (different phenotypes are produced by one genotype under different environmental
conditions).
Several distinct genetically controlled color morphs of Nezara viridula (Hokkanen 1986, Ohno and
Alam 1992, Musolin 2012; see Chapter 7), wing size polymorphism in many aquatic and semi-aquatic
Heteroptera (Saulich and Musolin 2007a), and all cases of sexual dimorphism, can be considered exam-
ples of genetic polymorphism.
Wing polymorphism recently was reported in the Neotropical genus Braunus Distant (Pentatomidae).
However, degree of manifestation, nature (i.e., genetic or environmental polymorphism), and control
mechanism are not known, as yet, because most species of Braunus are known from only few specimens
(Barão et al. 2016).